Device for operating a gas-discharge lamp

ABSTRACT

A device for operating a gas discharge lamp (11) which is triggered by pulses which are transmitted by a starting device (14). In order to isolate the electrical components of a ballast (12) or a power supply apparatus (10) during the starting process, a reactor (13) which is constructed as a saturable reactor is provided in the ballast. The inductance of the saturable reactor is reduced by the operating current flowing after starting of the lamp (11). The device according to the invention is particularly suitable for starting high-pressure gas discharge lamps, the starting power of the lamp (11) made available by the starting device (14) being made virtually completely available.

PRIOR ART

The invention proceeds from a device for operating a gas discharge lampaccording to the generic concept of the patent claim. GermanOffenlegungsschrift 3,929,029 discloses such a device in which a gasdischarge lamp is connected to a power supply apparatus via a ballastwhich contains a reactor. Furthermore, a device for starting the gasdischarge lamp is directly connected to the lamp. The reactor containedin the ballast fixes the current flowing when the gas discharge lamp isin operation, for example, or limits at least the current to aprescribed maximum value.

The starting device makes available one or more trigger pulses whoseenergy must suffice for reliable starting of the gas discharge lamp. Inthe known device, it cannot be ruled out that a certain portion of thestarting power is coupled into the ballast and is therefore no longeravailable for starting the lamp.

It is the object of the invention to specify a device for operating agas discharge lamp, in which the starting power applied by a startingdevice is made available as completely as possible for starting a gasdischarge lamp.

SUMMARY OF THE INVENTION

The above object is achieved, according to the invention, by a devicefor operating a gas discharge lamp having a ballast for the power supplyof the lamp, which ballast contains a reactor connector in series withthe lamp, and having a starting device connected to the lamp, andwherein the reactor is a saturable reactor whose inductance is reducedby the lamp operating current flowing after starting or ignition of thelamp.

ADVANTAGES OF THE INVENTION

The device according to the invention has the advantage that thestarting power of the lamp that is made available by the starting deviceis made completely available, so that a cost-effective design of thestarting device is possible. Electrical components which are containedin the ballast do not need to be designed for the high starting voltagesproduced during the starting process.

The device according to the invention is particularly suitable forstarting high-pressure gas discharge lamps which require a comparativelyhigh starting voltage and a high starting power, especially when thelamp is at operating temperature.

BRIEF DESCRIPTION OF THE DRAWING

The device according to the invention is explained in more detail belowwith reference to the drawing wherein the FIGURE is a block circuitdiagram of the device according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The FIGURE shows a power supply apparatus 10 which provides the voltagesand currents required for the power supply of a gas discharge lamp 11.The power supply apparatus 10 is connected to the lamp 11 via a ballast12.

Provided for starting the lamp 11 is a starting device 14 whichtransmits a trigger pulse whose voltage and whose energy contentsuffices for starting the lamp 11. Starting the lamp 11 is triggered bya control device, not shown in the FIGURE, which also controls the powersupply apparatus 10, if necessary.

When the starting device 14 transmits one or more trigger pulses, apartfrom the lamp 11 the ballast 12 is also subjected to correspondingpulses. It is provided according to the invention that the reactor 13contained in the ballast 12 has a nonlinear characteristic. The reactor13 is designated below as a saturable reactor. This method ensures anisolation of the starting circuit containing the starting device 14 andthe lamp 11 from further electrical components of the ballast 12 and ofthe power supply apparatus 10 during starting of the lamp. The saturablereactor 13 is to be designed in this case such that for a low current,the maximum of which can be reached during the starting process owing tothe short voltage pulse, the inductance assumes a high value whichcorresponds to the value of the non-saturated reactor. The comparativelyhigh operating current flowing after starting of the lamp is intended,by contrast, to lead to saturation of the reactor 13 and thus to adecrease in its inductance. The supply of the lamp with electrical poweris therefore possible during burning operation without the essentiallimitation owing to the saturable reactor 13.

The saturable reactor 13 can be provided by a winding which issurrounded by magnetisable material which is at least partiallysaturated by the high magnetic field strength when the operating currentof the lamp 11 is flowing, so that the magnetic induction can no longerrise in proportion to the magnetic field strength.

We claim:
 1. A circuit arrangement for a gas discharge lamp, comprising:a gas discharge lamp; a starting device, for supplying trigger pulses tothe gas discharge lamp during starting, connected in parallel with thegas discharge lamp; and a ballast for the power supply of the lamp,which ballast contains a non-linear reactor connected to the lamp inseries with the lamp and the power supply, with the reactor being asaturable reactor whose inductance assumes a high value corresponding tothat of the non-saturated reactor during the starting of the lamp and isreduced by the lamp operating current flowing after starting of thelamp.